1. Field of the Invention
The present invention relates to a system and method for handling airflow in a paint booth.
2. Disclosure Information
Modern painting techniques routinely use a series of paint booth cells to prepare and finish the surface of items such as automotive vehicle bodies. Typically, a vehicle body is transported through a series of paint spray booths where the workpiece surface is prepared and primed and paint is applied, dried, and finished. Much of the priming, painting and finishing is commonly performed by automated equipment. During this process, some of the applied materials may not adhere to the vehicle, but appear as over-spray in the booth atmosphere. This over-spray must be removed from the paint spray booth for example, to keep it from falling back on the painted vehicle or from being inhaled by equipment operators. The paint over-spray is typically removed by providing a continuous airflow from a supply plenum above the paint spray booth, through the paint spray booth and out to scrubber equipment which removes paint particles before exhausting the air to the atmosphere.
It is recognized that varying airflow velocity at different locations within a paint spray booth yields beneficial results. Increasing airflow velocity next to paint booth walls and equipment minimizes paint adhesion to these surfaces. Reducing air velocity near substantially vertical portions of a vehicle body promotes paint adhesion to such surfaces. Where horizontal surfaces are to be painted, however, it is recognized that increasing the velocity of the airflow and paint spray impacting the horizontal surface produces better results.
The current invention improves the control the airflow within a paint booth by actively controlling the airflow upon generally horizontal surfaces to be painted. A secondary air supply plenum is enclosed within a primary air supply plenum, from which it receives its air supply. The secondary plenum is located directly above automatic paint spray equipment used to paint generally horizontal surfaces of the workpiece. An air velocity detector is installed underneath the secondary plenum outlet and sends a signal to a damper controlling air intake at the secondary plenum inlet. The air velocity over generally horizontal workpiece surfaces is dynamically adjusted in real time to optimal values by using said damper to control the amount of air admitted into the secondary plenum, based at least in part on the air velocity detected near the automotive paint spray equipment. Continuous measurement and adjustment of airflow velocity promotes consistency and painting efficiency.
U.S. Pat. No. 5,480,349 illustrates a system in which a secondary plenum receives air under pressure from the first plenum, and wherein the atmospheric pressure of air in the second plenum is measured and controlled by increasing the air supply to the first plenum. The present invention differs in several respects from the '349 patent. In particular, the present invention regulates airflow based on air velocity, which is more accurate and reliable than a system based on measuring air pressure. Further, the '349 patent dynamically adjusts the amount of air supplied to the primary plenum only; the amount of air supplied to the secondary plenum is controlled by a set of sliding plates positioned during a setup process. In contrast, the current invention does not vary the amount of air supplied to the primary plenum, but actively controls the amount of air supplied to the secondary plenum directly, based at least in part on air velocity measured beneath the secondary plenum. The present invention permits more accurate adjustments of airflow at targeted locations within the paint booth and is less susceptible to changes in atmospheric pressure and other variable conditions commonly encountered in multi-cell paint booth systems. The present invention promotes consistent downdraft at key areas in a paint booth cell even when used in conjunction with airflow handling systems that dynamically adjust air supplied to primary plenums in order to balance lateral airflows between cells in multi-cell systems.